46 E. RAY LANKESTER. 
to a pair of nerve-ganglia. I have since found that these 
supposed nerve- ganglia are the white bodies’ observed in con- 
nection with the eye and optic ganglia in adult Cephalopoda 
Dibranchiata. I am disposed to regard them as atrophied or 
suppressed nerve-ganglia, pr obably » representing the cephalic 
ganglia of other Mollusca which develop in the same position 
and essentially in the same way as do these white bodies. In 
fig. 10 the section passes below the eye, through one of these 
invaginations which is still open. I have numerous drawings 
of the invagination in the living state at this and later periods. 
The mass of tissue (NG) at the base of the optic invagination 
has the form of a peduncle. It does not, I believe, arise in 
connection with the optic invagination, but is formed in the 
mesoblastic mass of cells. It is this optic peduncle which 
gives rise to the great optic ganglion on each side, and to the 
other smaller ganglionic masses. 
In fig. 11, a section at a later period is seen where the 
nerve-ganglion has grown to a large size and is definitely 
dividing itself into lobes. ‘The white body (ws) is seen 
still of large size. In living specimens of about this age the 
“white bodies ”’ are very obvious and prominent, whilst the 
large mass of the optic peduncles present two very distinct 
lobes on each side. In subsequent growth the mass (NG) 
encroaches upon the white body, which becomes flattened 
out, and no longer advances in growth at the same rate as the 
surrounding parts. Sections at this period lead to the con- 
clusion that the optic ganglion is nourished at the expense of 
the material of the White Body, aud finally when the eye and 
optic ganglion have attained an enormous proportionate size 
in comparison with the other parts of the embryo (a few days 
before birth), the white body is seen as a much reduced mass 
of embryonic (undifferentiated) cells occupying the angle be- 
tween the eye and optic ganglion and squeezed into obscurity 
between the two. A full series of drawings from the sections 
are needed to elucidate the history of the white body and 
optic ganglion, but the examples selected from a large num- 
ber in my possession, viz., figs. 10 and 11, must suffice for the 
present. 
That so important an organ as the cerebral or super-cso- 
phageal ganglion of Mollusca should disappear or become 
rudimentary in Cephalopoda must appear somewhat startling, 
as also the fact that nerve ganglia should develop from so- 
called mesoblast. ‘This last phenomenon I believe to be in 
accordance with the general law which relegates to ‘ meso- 
blast ” various structures originally either epiblastic or hypo- 
blastic, when the tendency to direct development can be 
